Method of making secondary-battery plates.



UNITED STATES PATENT OFFICE.

BERTHOLD Kl lETTNER, OF LONDON, ENGLAND.

METHOD OF MAKING SECONDARY-BATTERY PLATES.

SPECIFICATION forming part of Letters Patent No. 681,329, dated August27, 1901.

Application filed October 25, 1900.

T at whom it may concern:

Be it known that I, BERTHOLD KiiETTNER, electrical engineer, of AlfredPlace, Bedford Square, London, W. 0., England, a subject of the Emperorof Germany,have invented certain new and useful Improvements in theManufacture of Secondary-Battery Plates, of which the following is aspecification.

This invention relates to improvements in the manufacture ofsecondary-battery plates, the object of which is to render such platesstronger, lighter, and more durable and to increase their efliciency.

My invention relates especially to the paste or active material employedin such plates, and in the preparation of this active material I employfinely-divided oxids of lead, preferably litharge, to whichfinely-divided lead may be added, mixed with a solution of a solublesilicate or silicates, such as sodium or potassium silicate, to form apaste or plastic compound. This paste after application to a leadconducting sheet is placed under slight pressure and is then dipped intoa very dilute ammonium solution, preferably ammonium sulfate. The plateis dipped into this hardening solution before it has dried or set and isleft in the solution a considerable time, say from twenty-four toforty-eight hours. Chemical reaction is set up and the solution becomesstrongly alkaline through dissolved ammonia. The chemical changes mayroughly be represented as follows in the case of an ammonium-sulfatesolution:

of the hardening solution upon the uncombined silicate contained in theplate cannot be adequately represented in any simple for- A chemicalaction takes place, howmula.

Serial No. 34,367- (No specimens.)

ever, which results in the free silicate being dissolved in the solutionvery slowly and small quantities of a gelatinous substance re- 5 5 sult,which sink to the bottom of the vat in which the plates are placed. Thismaterial may be spoken of as gelatinous silica, and the material isformed very slowly and in small flakes only until the silicate ispracti- 6o cally entirely removed. The action may be represented veryroughly by the following formula:

The chemical action thus indicated is not, however, necessarilycompleted in the plate, and. various hydrated compounds of silica may beformed in the solution as the sodium after the process is in combinationwiththe lead or lead compounds.

The contact between the lead grid and the active material is very close,as the surface of the lead conducting sheet is slightly acted upon bythe paste, so that there is a distinct 8o union between the two, givingthe best possi ble electrical contact. the lead sulfate formed in theplate as above described, the surface of the lead conducting sheet beingalso slightly sulfated. The plate 8 5 so prepared can be reduced toporous lead to form the positive plate of a secondary battery or may bedirectly formed in the usual manner into lead peroxid without requiringany prior reduction to pure lead. It is also found that 0 forming takesplace from the grid outward and not from the surface of the activematerial, and it may thus be at once seen when the plate is formedthroughout.

The reducing and forming of the plates 5 may be effected in the usualmanner; but I find it advantageous to reduce the positive plate in asolution of ammonium sulfate and to oxidize the negative plate in dilutesulfuric acid, or both plates may be treated I00 simultaneously in aslightly-acid solution of sulfuric acid and ammonium sulfate.

Plates having the active material prepared in the manner described showvery This action is due to ployed in making the paste. hard and coherentplate is obtained by the slight expansion and contraction during chargeand discharge, and the stresses commonly set up in secondary-batterycells are thus reduced. The exact amount of expansion can be regulatedin manufacture by Varying the mixture of oxids employed, which all forma setting paste with the soluble silicate. In the preparation of thepaste for these plates the lead employed may vary from purefinely-divided lead to' lead peroxicl, or any mixture of the oxids maybe used according to the circumstances. If pure lead is employed, thenegative plate expands to the largest possible extent in conversion toPbO This expansion decreases with the addition of oxids until theminimum of expansion is reached,when PbO itself is em- In all cases atreatment above described, and a grid in the sense of a support for theplate is not necessary. All that is required in order to provide for arapid discharge of the cell is a lead conducting sheet.

WVhat I claim as my invention, and desire to secure by Letters Patent,is-

1. In a method of making secondary-battery plates, mixing lead oxidswith a solution of a soluble silicate to form a paste, making the pasteinto a plate and dipping the plate in a dilute solution of an ammoniumsalt, substantially as herein described.

2. A method of making secondary-battery plates, consisting in mixinglead oxids with a solution of a soluble silicate to form a paste, makingthe said paste into the form of a plate, dipping the plate into a dilutesolution of an ammonium salt, removing it and placin git in a secondsolution of greater strength and afterward forming the plate,substantially as herein described.

In Witness whereof I have set my hand in the presence of two Witnesses.

BERTI-IOLD KUETTNER.

In presence of- FRANK WILLIAM PATTISON, WILLIAM J AMES Cox.

